Hi Raimo,
As an engineer who has been working two decades for a spark plug company, I want
to add a few thoughts about your engine problem:
A misfiring spark plug, cannot cause detonation.
A single misfiring spark plug on one cylinder cannot cause the high level of
vibration
you have experienced.
There are only two cases where a spark plug can cause detonation: the first one
is if you are using a spark plug with a too hot heat rating. In this case, the
nose core and the center electrode of the spark plug becomes red hot and ignite
the fuel mixture even without a spark. The second case is when the spark plug
is not torqued enough, becomes loose so that the heat transfer from the shell
to the cylinder head is limited, causing the spark plug to become very hot.
Both cases will cause preignition and possible detonation.
I assume you were using the right spark plug type and that your blue spark plug
was found to be tighten correctly. So in my opinion, the very hot blue spark
plug you got was not the cause but the consequence of another phenomenon,
probably
preignition and/or detonation, caused by something else.
The two main causes of detonation are: a too lean mixture and a too low octane
fuel. This is were I would direct my investigation.
Preignition and detonation may seriously damage all combustion chamber parts
such
as piston, rings, and valves.
After such a problem I would ground the aircraft until the root cause is found,
and I would carefully check the above parts for damage. Before removing the
cylinder,
I would perform a compression check and a boroscope inspection of the
combustion chamber.
Hope that helps.
Remi Guerner
F-PGKL
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